The present invention relates to a semiconductor integrated circuit device and to the integrated circuit technology useful for fabricating a motor drive control circuit which controls the operation of an electric motor for example.
FIG. 3 shows a motor drive control circuit, and such a control circuit is disclosed in Japanese Patent Application No. 63-294290. In the figure, indicated by H1, H2 and H3 are Hall elements which detect the rotational position of the motor magnetically. The Hall elements H1, H2 and H3 produce rotational position signals u, v and w as shown by FIGS. 4(A),4(B) and 4(C),and the signals are fed to Hall amplifiers 2, 3 and 4, respectively.
The Hall amplifiers 2, 3 and 4 amplify and shape the detected signals u, v and w, and deliver the resulting signals to a matrix circuit 6 of the next stage. From the received signals u, v and w, the matrix circuit 5 produces phase switch signals U, V and W each having a high level H, mid level M and low level L as shown by FIGS. 5(A), 5(B) and 5(C), and delivers the signals U, V and W to three-level differential circuit 9 of the next stage.
The three-level differential circuit 9 consists of a first three-level differential circuit made up of three npn bipoler transistors Q1, Q2 and Q3 and a second three-level differential circuit made up of three pnp bipoler transistors Q4, Q5 and Q6, and currents 101 and 102 are controlled by a current control circuit 8. In the three-level differential circuit 9, the npn transistors Q1, Q2 and Q3 drive output circuits A1', A3", and A5 when the phase switch signals U, V and W are at the high level H, and these transistors are cut off when the signals are at the mid level M or low level L. The pnp transistors Q4, Q5 and Q6 are cut off when the phase switch signals U, V and W are at the high level H or mid level M, and these transistors are made conductive when the signals are at the low level L.
Accordingly, the transistors Q1 and Q5 are conductive during the period between t.sub.0 and t.sub.1, in FIG. 4, causing the output circuit A1' on the voltage source Vcc side formed of transistors Q30 and Q31 and the output circuit A4' on the ground side (having the same transistor configuration as A2') to operate to feed a drive current to motor windings(coils) L1 and L2.
During the period between t.sub.1 and t.sub.2, the output circuit A1' on the voltage source side and the output circuit A6' on the ground side operate to feed a drive current to motor windings (coils) L1 and L3. In this manner, the transistors Q1-Q6 operate in accordance with the levels of the phase switch signals U, V and W to drive selectively the output circuits A1', A3' and A5' on the voltage source side and the output circuits A2', A4' and A6' on the ground side. As a result, on the waveform diagram of FIG. 4, a drive current flows in the motor windings (coils) L2 and L3 during the period between t.sub.2 and t.sub.3, a drive current flows in the motor windings L2 and L1 during the period between t.sub.3 and t.sub.4, a drive current flows in the motor windings L3 and L1 during the period between t.sub.4 and t.sub.5, and a drive current flows in the motor windings L3 and L2 during the period between t.sub.5 and t.sub.6.
In the circuit arrangement of FIG. 3, each output circuit on the voltage source side (e.g., A1') consists of a pnp transistor Q30 (pre-driver transistor) and an npn output transistor Q31, and therefore the output circuit has its load current capacity limited by the saturation voltage of the transistors Q30 and Q31.
The motor drive control circuit is used for floppy disk drive units and hard disk drive units, which are often designed to operate on a low power voltage such as 5 volts or 3 volts for the achievement of compactness and portability. In the trend of low voltage operation, the above-mentioned saturation voltage of the output circuit is no more negligible.
In dealing with this situation, a technique of applying an emitter voltage higher than Vcc to the pre-driver transistor is disclosed in Japanese Patent Application No. 1-117685 (publicized on May 10, 1989).